Liakopoulos Dimitris, Kusch Justine, Grava Sandrine, Vogel Jackie, Barral Yves
Institute of Biochemistry, Swiss Federal Institute of Technology, ETH-Hoenggerberg, HPM, CH-8093 Zürich, Switzerland.
Cell. 2003 Feb 21;112(4):561-74. doi: 10.1016/s0092-8674(03)00119-3.
Spindle alignment is the process in which the two spindle poles are directed toward preselected and opposite cell ends. In budding yeast, the APC-related molecule Kar9 is required for proper alignment of the spindle with the mother-bud axis. We find that Kar9 localizes to the prospective daughter cell spindle pole. Kar9 is transferred from the pole to cytoplasmic microtubules, which are then guided in a myosin-dependent manner to the bud. Clb4/Cdc28 kinase phosphorylates Kar9 and accumulates on the pole destined to the mother cell. Mutations that block phosphorylation at Cdc28 consensus sites result in localization of Kar9 to both poles and target them both to the bud. Thus, Clb4/Cdc28 prevents Kar9 loading on the mother bound pole. In turn, asymmetric distribution of Kar9 ensures that only one pole orients toward the bud. Our results indicate that Cdk1-dependent spindle asymmetry ensures proper alignment of the mitotic spindle with the cell division axis.
纺锤体定向是指两个纺锤体极被导向预先选定的相对细胞末端的过程。在芽殖酵母中，与后期促进复合物（APC）相关的分子Kar9是纺锤体与母-芽轴正确定向所必需的。我们发现Kar9定位于预期的子细胞纺锤体极。Kar9从纺锤体极转移到细胞质微管，然后微管以肌球蛋白依赖的方式被引导至芽。Clb4/Cdc28激酶使Kar9磷酸化并在注定进入母细胞的纺锤体极上积累。在Cdc28共有位点阻断磷酸化的突变会导致Kar9定位于两个纺锤体极，并将它们都导向芽。因此，Clb4/Cdc28阻止Kar9加载到与母细胞相连的纺锤体极上。反过来，Kar9的不对称分布确保只有一个纺锤体极朝向芽。我们的结果表明，依赖细胞周期蛋白依赖性激酶1（Cdk1）的纺锤体不对称性确保有丝分裂纺锤体与细胞分裂轴的正确定向。
